A Review of Anti-Cancer and Related Properties of Lichen-Extracts and Metabolites

Background: Lichens are a composite consortium of a fungus and an alga. The symbiotic organisms are naturally equipped with distinct characteristics as compared to constituting organisms separately. Lichens, due to their peculiar anatomy and physiology, are the reservoir of more than 600 unique secondary metabolites, also known as ‘lichen substances’. Since ancient times, many ethnic groups from various parts of the world have known about the applications of lichens as major provenance of food/fodder, medicine, dyes, spices, perfumes, etc. Lichen substances have shown impressive antioxidant, antimicrobial, antiviral, anti-tumor, and antiinflammatory activities under experimental conditions. Usnic acid, a well-known metabolite found in several species of lichens, possesses potent antioxidant and anti-inflammatory activities. It also has significant antiproliferative potential, as revealed through testing in different cancer cell lines. Atranorin, Lecanoric acid, Norstictic acid, Lobaric acid, Stictic acid, Ramalin, Gyrophoric acid, Salazinic acid, Protolichesterinic, and Fumarprotocetraric acid are some of the other purified lichen-metabolites with potent anti-cancer activities. Objective: This study presents an overview of lichen-derived extracts and compounds showing anti-cancer (or related) properties. Method: The review comprehends different studies (in vivo and in vitro) backing up the possibility of lichenextracts and metabolites towards their use as antioxidant, anti-proliferative, anti-inflammatory, and Epithelialmesenchymal transition (EMT) -inhibiting agents. Results: Various studies carried out to date show that lichen-extracts and metabolites have a range of anti-cancer and related properties that include anti-oxidative, anti-inflammatory, anti-proliferative, pro-apoptotic, and the potential of inhibition of cancer-associated EMT that is responsible for drug resistance and metastasis of cancer cells in a substantial proportion of cases. Conclusion: Lichens are the repertoire of a plethora of lichen-metabolites with significant anti-cancer potential. However, some of the critical ‘anti-cancer related’ properties, such as the ability of EMT-inhibition and the potential of induction of apoptosis, are relatively less studied for several lichen compounds. Additionally, many lichen compounds need to be purified at a larger scale to explore their anti-cancer potential.